Vestibular

Question 1

What is the vestibular system?

What connects the input and output?

Answer 1

A system that has inputs and outputs (reflexes) to help maintain balance and posture

CNS connects the inputs to the output, CNS tends to generate the output (as outputs are usually reflexes)

Question 2

What are the 3 main inputs of the vestibular system?

What are the 2 main outputs?

Answer 2

Visual
Proprioception - pressure on parts of the body tells you where the structures are in space
Vestibular information - info coming in from the inner ear detecting rotation and gravity of the head

Ocular reflex - stable gaze
Postural control - stable posture

Question 3

What is the vestibular organ and how does it detect rotation and movement?

Answer 3

Vestibular organ = posterior part of the inner ear

They contain hair cells to transduct stimuli into nervous impulses

Question 4

What are the structures within the vestibular organ?

Answer 4

Contains:
The vestibule (entrance of the inner ear) - formed by the utricle and saccule, both joined by a conduit
Saccule is also joined to the cochlea (auditory organ)
3 semicircular canals - anterior, posterior and lateral. They have an ampulla on one side, and joined to the utricule on the other

Question 5

What angle do the anterior and posterior semi-circular canal form when they meet?

What is the purpose of this?

Answer 5

A right angle - 90 degrees

Forms different planes so movement in various directs can be detected - certain structures stimulates for specific head movements

Question 6

What are the vestibular hair cells called?

Answer 6

Different to the hair cells in the cochlea for hearing

The vestibular hair cells are called kinocilia and stereocilia

Hair cells arranged like a foot - big toe = kinocilia, the other toes getting smaller = stereocilia

They are found in the utricle, saccule and the 3 semicircular canals

Question 7

What is the function of the hair cells found in the semi-circular canals?

Answer 7

When the head moves, it also moves the liquid in our ears (endolymph)

Movement of liquid causes movement of the hair cells

Depending on strength of movement and whether the stereocilia move towards (excitation) or away (inhibition) from the kinocilia, the cilia allow for depolarisation

Greater movement = greater depolarisation

Question 8

What organs are the utricle and saccule called?

Answer 8

Otolith organs

Question 9

Where are the hair cells in the otolith organs found and how are they different to the ones found in the semicircular canals?

Answer 9

The hair cells are on the maculae and placed horizontally on the utricle, vertically on the saccule

The hair cells have a gelatinous matrix and otoliths (carbonate crystals) on top to help with the deflection of the hairs (using its weight)

Question 10

So do the semicircular canal hair cells contain otoliths (crystals)?

Answer 10

No, and they should not

If they do, they can cause abnormal symptoms / conditions e.g. vertigo

Question 11

Where are the hair cells located in the semicircular canals?

What kind of fluid is found in the semicircular canals?

Answer 11

In the cristae of the ampulla

Endolypmh (fluid high in K+), less viscous than the gel found in the otolith organs

The cells are surrounded by cupula, which helps deflection of the cilia

Question 12

What are the 3 planes of the 3 semicircular canals?

Answer 12

Anterior and posterior = 90 degree angle where they meet

Lateral canals are horizontal to the other canals

Question 13

What is the vestibular nerve?

What are the names of the 4 main vestibular nuclei?

Where do the vestibular nuclei project to?

Answer 13

CN VIII - carries sensory info from inner ear to brain

Superior, Lateral, Medial, Inferior

Vestibular nuclei have projections to the: spinal cord (reflexes), cerebellum (feedback whether movement is co-ordinated), extraocular muscles (eye movement response), centres for cardiovascular and respiratory control (ANS responses)

Question 14

Summarise the vestiibular pathways, starting from input into the vestibular system:

Answer 14

Input via hair cells in the vestibular system

Info transduced and travels to vestibular nuclei

Superior and lateral vestibular nuclei = info processed in vestibular cortex

Lateral medial and inferior vestibular nuclei = vestibulospinal reflex (posture), vestibulocerebellar reflex (CO2 monitoring), vestibulo-ocular reflex (eye movement in compensation for head movements)

Question 15

What and where is the vestibular cortex?

What is the vestibular cortex responsible for?

Answer 15

Not one specific area - multiple cortical areas participate although main processing = in parietal lobe (Parieto-insular Vestibular Cortex - PIVC)

Processes / co-ordinates eye and head movements

Question 16

What are the 3 vestibular system functions?

Answer 16

Detect and inform about head movements
Keep images fixed on the retina during head movements
Maintain postural control

Question 17

How does the vestibular system work to carry out its functions i.e. detect head movements?

Answer 17

Hair cells have a resting potential, this has a basal nerve discharge

Movement of the head = movement of the inner ear fluid = movement of cilia

The movement of stereocilia towards kinocilia = excitation and depolarisation of the cell = increased nerve discharge

Movement of stereocilia away from kinocilia = inhibition and hyperpolarisation = reduced nerve discharge

So when moving your head, whilst in one ear you get excitation, in the other you get inhibition

Question 18

How do the otolith organs work / detect head movement?

Answer 18

Otolith movement is detected by linear acceleration and tilt

Utricle = horizontal movement

Saccule = vertical movement

Question 19

How do the semicircular canals work / detect head movement?

Answer 19

Detects angular acceleration

Movement of the head = movement of the endolymph = displacement of the cupulla = deflection of the hair cells

Signal on the nerve = velocity

Question 20

How do the semicircular canals work in pairs?

Answer 20

Both the lateral planes work together - i.e. on either side of the ear
Anterior from one side with posterior from opposite side work together i.e. right anterior and left posterior, left anterior and right posterior

Question 21

What are the 2 main reflexes and their functions?

Answer 21

Vestibulo-ocular reflex (VOR) - fastest reflex in the body, keep eyes fixed on image while head is moving
Vestibulo Spinal Reflex (VSR) - maintain posture and stay upright, works when we lose balance

Question 22

How does the vestibulo-ocular reflex (VOR) work?

Answer 22

Image stays fixed on retina

Connection between vestibular and oculomotor nuclei

Works by having the eye move in the opposite direction of the head but at the same velocity and amplitude e.g. eyes move to the left and head moves to the right

Question 23

How does the vestibulo spinal reflex (VSR) work?

Answer 23

Motor neurons to the limb muscles (lateral tract)

Motor neurons to the neck and back muscles (medial tract)

Postural control and avoidance of falls = head movement detected by vestibular organ and is transmitted to the vestibular nuclei and spinal cord, so compensatory body movement is made

Question 24

How can the vestibular system be assessed in a patient?

Answer 24

Anamnesis - history

Test posture and gait - posturography = recording of walk, questionnaires

Cerebellar function - typical neurological assessments

Eye movements - clinical testing, or recording eye movements

Question 25

What are some specific vestibular tests to assess how the vestibular organ is working?

Answer 25

Caloric test
vHIT (video vestibular impulse test)
VEMP (vestibular evoked myogenic potential)
Rotational test

Question 26

How do each of these tests below work?

Caloric test
vHIT (video vestibular impulse test)
VEMP (vestibular evoked myogenic potential)
Rotational test

Answer 26

Caloric test - stimulate inner ear with different temperatures which should generate nystagmus (involuntary eyemovement)

vHIT - test both ears simultaneously, measures function (good for assessing recovery, not finding the problem)

VEMP - measures connection between vestibular system and the neck

Rotational test - rotating chair and detection of vestibular response to that

Question 27

What imaging techniques can be used to look into the vestibular system?

Answer 27

CT Scans, MRIs

Question 28

What is the purpose of a symptoms and impact assessment?

Answer 28

Although dysfunction may be small, it may have a huge impact on their life, and vice versa
Helps determine next step in diagnosing / treatment plan

Question 29

What are the main symptoms of balance disorders?

Answer 29

Vertigo - perception of rotation, feeling of things spinning around (everything moving around like a carousel)
Dizziness

Question 30

How can disorders of the vestibular system be categorised?

Answer 30

Location of affected structure - peripheral or central

Evolution of signs and symptoms - acute, recurrent, intermittent, progressive

Question 31

What are some peripheral and central vestibular disorders?

Answer 31

Peripheral = issue with the inner ear and/or VIII before it goes into the brain stem e.g. vestibular neuritis, BPPV (benign paroxysmal positional vertigo), Meniere’s disease, unilateral and bilateral vestibular hypofunction

Central = e.g. stroke, MS (multiple sclerosis), tumours

Question 32

What are some acute, intermittent, recurrent, and progressive vestbular disorders?

Answer 32

Acute = Vestibular neuritis (labrynthitis), stroke
Intermittent = BPPV (benign paroxymal positional vertigo
Recurrent = Meniere's disease, migraine
Progressive = Schwannoma vestibular, degenerative conditions e.g. MS

Question 33

What are some non-vestibular causes for dizziness?

Answer 33

Heart disorders
Presyncopal episodes
Orthostatic hypotension
Anaemia
Hypoglycaemia
Psychological disorders
Gait disorders